Switched-mode power supplies have been in widespread use for several decades. An important component of such power supplies is the DC-to-DC converter. These converters accept power as a first direct current (DC) voltage (typically unregulated) and provide power for use by one or more electronic devices at a second, regulated DC voltage. The input DC supply is converted into a series of pulses with operating frequencies in the tens or hundreds of kilohertz. Regulation is typically achieved by varying the width and/or duty cycle of the individual pulses. A switching device amplifies and feeds the pulse train into a low-pass filter at the output of the converter, thus providing a regulated DC voltage at the output of the filter.
The control signal used to vary the pulse width is generally an error signal derived from the difference between the output DC voltage and a precision reference voltage. Identifying how to generate such a control signal with a compensator circuit involves a number of difficult design problems. Both the filter present at the converter output and the load present at the filter output are generally complex loads that behave non-linearly. Attempting to regulate the voltage of the converter output linearly with a simple difference signal can result in a filter output voltage that overshoots and/or undershoots the target regulation point, and may further have an unacceptable ripple component. A type II compensator can provide a stable, non-linear control signal, but in such designs it is important to match the behavior of the compensator to the filter present at the output of the converter to achieve accurate DC voltage regulation. This may not always be possible, particularly where the DC-to-DC converter is implemented as a single, general-purpose integrated circuit with unknown external filter components. Further, load current sensing rather than voltage sensing may be required by such compensators, and such current sensing may not always be available or practical.
It should be understood that the drawings and corresponding detailed description do not limit the disclosure, but on the contrary, they provide the foundation for understanding all modifications, equivalents, and alternatives falling within the scope of the appended claims.